Devices of this type are generally designed to meet the respiration needs of a person operating at a given level of effort for a well defined or specified period. For each apparatus therefore, this design determination leads to seeking minimum weight of superoxide corresponding to a maximum rate of use, which implies the best correlation of various parameters, such as reactivity of the superoxide, its temperature behavior, the size and shape of the superoxide pellets and particularly the structure of the regenerating charge.
Oxygen chemical generation breathing devices are subject at times to intense regeneration conditions when the respiration level reaches an output above 35 liters per minute (and even 70 liters/minutes, for a few minutes for carbon dioxide contents between 4 and 5%). Under these conditions, the particles of solid reagents with a potassium superoxide base are the site of reactions of the superoxide with carbon dioxide and water vapor. These reactions which release oxygen are very exothermic, subjecting the reagent particles to very high temperatures that can reach 200.degree. to 300.degree. C.
It is known that the superoxide reacts more quickly with carbon dioxide than with water vapor, which corresponds to a more accelerated fixing of the CO.sub.2, whereas pure potassium superoxide generates oxygen from water vapor by forming relatively fusible potassium hydroxides. Thus, when a bed of superperoxide particles for regeneration of respiration gases is subjected to the action of a gas corresponding to a high respiratory rate, it is found that the layer of the regeneration product at the upstream end of the device, quickly becomes carbonated and the particles retain their shape and mechanical properties, while downstream from this layer the regeneration particles receive a considerable amount of water and are quickly deformed and made deliquescent.
If this operation is continued, this degradation evolves to fusion of the particles, thus causing a partial collapse of the regenerating charge, with formation of a compact fused mass offering a very reduced reactive surface to the gas and, in addition, empty cavities of reagent which often constitute preferred channels taken by the gas to be regenerated and in which the carbon dioxide is treated very imperfectly. Although a considerable proporation of the reactive product still remains in the bed of regenerating particles, a rapid increase is observed in the carbon dioxide content of the effluent gas corresponding to a great reduction in the overall reactivity of the bed; this reduction of the level of purification of the gas is often accompanied by a great increase in the pressure drop of the particle bed. Consequently, there is a poor use of the superperoxide which does not achieve its reactive potential.
Efforts have been made to mitigate this drawback by giving the cartridge such a structure that the gas passes through a small thickness of the superoxide at a slow speed, or by dividing the charge nto small fractions by numerous metal partitions that come in contact with the wall. These efforts led to complex structures in which the weight of the nonreactive material was relatively great; their cost is high and filling cartridges with them is rather clumsy and poorly suited to automation.
Recently, a means was proposed making it possible to eliminate the excessive increase in the pressure drops of the potassium superoxide during intense regeneration conditions. According to U.S. patent application Ser. No. 460,542 now U.S. Pat. No. 4,490,272 a certain proportion of alkaline-earth oxide in the powder state is incorporated in the potassium superoxide before granulation or pelleting; degradation of the particles caused by water vapor is slowed down. Calcium oxide is particularly effective in obtaining this result. However, this addition of lime has an impact on the amount of generable potential oxygen, the latter being limited because it dilutes the superoxide.
This means is not fully satisfactory when it is desired to make relatively thick beds of reactive mixtures of as thick as about twenty centimeters, which work at a high kinetic level, with an extended regeneration period and practically total use of the reactive potential of the solid.